With a very long launch rail, acceleration to mach 1 is not unreasonable at 6 G. From there a scramjet could get it fast enough to engage my plasma envelope drive. By manipulation of the plasma envelope only the very tip of the ship would be a heat shield. You can push the plasma back and away at the same time, causing both thrust and shielding. Now power..... that is another can of worms.

_________________Let not the bindings of society hold you back from improving it.... the masses follow where the bold explore.

Again, you're talking about slamming into the sound barrier. While this might compression ignite a scramjet, it's just as likely to create instant drag losses that quickly drop it below the sound barrier again, and probably destablize it to tumble out of control. Also, you're not going to get it up to orbital velocity in the atmosphere with your ramjet, so it'll still need a rocket stage. This is a bit more reasonable, though, as it's scaled low enough to accieve with a fairly short barrel.

_________________"You can't have everything, where would you put it?" -Steven Wright.